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The present invention relates generally to radio frequency and microwave circulators, and more specifically to a junction-type stripline circulator providing enhanced performance in a more compact device configuration.
Radio Frequency (RF) and microwave circulators are known that employ a DC-biasing magnetic field generated in ferrite material enveloping a conductor to provide at least one non-reciprocal transmission path between signal ports on a network. A conventional junction-type stripline circulator comprises at least one junction configured as an interface between the signal ports. Each junction of the junction-type stripline circulator typically includes two (2) permanent magnets, two (2) ground plane portions disposed between the magnets, two (2) ferrite disks disposed between the ground plane portions, a dielectric constant medium disposed between the ferrite disks, and a conductor sandwiched between the ferrite disks and patterned to correspond to the transmission paths between the signal ports. The permanent magnets are configured to generate a DC-biasing magnetic field in the ferrite disks, thereby providing the desired non-reciprocal operation of the transmission paths between the signal ports on the network.
One drawback of the conventional junction-type stripline circulator, particularly multi-junction stripline circulators comprising a plurality of junctions connected in cascade, is that it frequently exhibits degraded electrical performance. This is because the successive junctions of the multi-junction stripline circulator are typically interconnected by respective microstrip transmission lines. Further, an impedance matching structure is typically required at each junction-to-transmission line transition of the circulator. For example, a multi-junction stripline circulator comprising two (2) junctions may include a single transmission line interconnecting the junctions and two (2) impedance matching structures at respective ends of the transmission line. As a result, there is often significant sensitivity of the signal phase and Voltage Standing Wave Ratio (VSWR) amplitude between the junctions of the circulator. Moreover, such a junction-type stripline circulator configuration comprising a transmission line between successive junctions of the circulator and multiple impedance matching structures at the junction-to-transmission line transitions can significantly increase the size of the overall device.
It would therefore be desirable to have a junction-type stripline circulator that can be used in RF and microwave applications. Such a junction-type stripline circulator would be configured to provide enhanced performance in a smaller device configuration.
In accordance with the present invention, a junction-type stripline circulator is provided in which performance is enhanced while the size of the overall device is reduced. Benefits of the presently disclosed invention are achieved by configuring the junction-type stripline circulator to include a single permanent magnet and a dual ferrite component that are employed by successive junctions of the circulator, and a single impedance matching structure coupled between the successive junctions of the circulator.
In one embodiment, the junction-type stripline circulator comprises a compact dual element cascade circulator including a plurality of junctions connected in cascade to provide a plurality of non-reciprocal transmission paths between signal ports on a network. The plurality of junctions comprises a single oblong permanent magnet, an oblong ground plane disposed near the permanent magnet, a dual ferrite component including two (2) oblong ferrite elements disposed near the ground plane, and a conductor sandwiched between the ferrite elements. A dielectric constant medium is disposed between the two (2) ferrite elements. Further, the conductor is patterned to correspond to the configuration of the transmission paths between the signal ports.
The conductor includes a plurality of conductor portions, and each junction of the dual element cascade circulator comprises a respective one of the conductor portions. Further, sections of the conductor between successive conductor portions are used to form single impedance matching structures for respective junction-to-junction transitions. In this embodiment, each impedance matching structure comprises a lumped reactance.
The dual element cascade circulator further includes a metal housing having an open top into which the plurality of junctions is disposed, and a metal cover configured to enclose the top of the housing to secure the junctions inside. The metal housing has a plurality of slots through which respective contact terminals of the conductor protrude to make contact with the signal ports on the network.
The plurality of junctions further comprises two (2) oblong pole pieces associated with the permanent magnet, and a cover return component. A first pole piece is disposed between the magnet and the ground plane, and a second pole piece is disposed between the base of the housing and the dual ferrite component. The cover return component is disposed between the cover and the permanent magnet.
In this embodiment, the combination of the ground plane, the dual ferrite component, and the conductor forms a Radio Frequency (RF) or microwave circuit configured to provide desired non-reciprocal transmission paths between the network signal ports. Further, the combination of the pole pieces, the permanent magnet, the metal housing, the cover return component, and the metal cover forms a magnetic circuit configured to generate a DC-biasing magnetic field in the dual ferrite component, thereby achieving the desired non-reciprocal operation of the transmission paths. Moreover, the two (2) pole pieces are configured to enhance the homogeneity of the magnetic field in the dual ferrite component, the cover return component is configured to provide an easy return path for the magnetic flux associated with the DC-biasing magnetic field from the ferrite elements to the permanent magnet, and each impedance matching structure is configured to avoid the reflection of energy between successive junctions of the circulator.
By configuring the compact dual element cascade circulator to include the single permanent magnet and the dual ferrite component that can be employed by successive junctions of the circulator, and the single impedance matching structure coupled between the respective successive junctions, the circulator achieves numerous benefits. For example, the performance of the dual element cascade circulator is enhanced. Particularly, by providing the single impedance matching structure between successive junctions, phase uniformity is improved, and both Voltage Standing Wave Ratio (VSWR) amplitude sensitivity and overall insertion loss are reduced. Other benefits include a more compact design due to the integral impedance matching structure, more consistent return loss values, more uniform DC-biasing magnetic fields, better power handling due to improved distribution of heat in the dual ferrite component, and quicker and more uniform magnetic field settings because the oblong permanent magnet design allows the use of a c-coil degausser, which generally cannot be used with conventional junction-type stripline circulator designs.
Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows.